Separation of materials of different specific gravities



Dec. 8 1942. F. L. GRIII=FITHSETAL ,304 2 SEPARATION OF MATERIALS OFDIFFERENT SPECIFIC GRAVITIES Filed Jan. 18, l940 INVENTORS:

ATTORNEYS.

W TNESSES: w I Franklouis firifiiihs 25a M FrederLck Charles Myer,

Patented Dec. 8, 1942 UNITED STATES PATENT OFFICE SEPARATION OFMATERIALS OF DIFFERENT SPECIFIC GRAVITIES deceased Application January18, 1940, Serial No. 314,422 In Great Britain January 6, 1939 3 Claims.

This invention relates to improvements in the methods and apparatus forthe separation of materials of different specific gravities, and inparticular to the separation of coal from its impurities, by the Chancemethod described in British Patent No. 119,038 and U. S. Patent No.1,224,138, granted May 1, 1917that is to say, the method in which thematerials are introduced into a liquid mass or separation mediumcomprising a suspension of sand in a liquid (which is generally water,and is hereinafter so designated), which is so arranged that itseffective density is great enough to cause some materials, such as coal,to float, while others, such as slates (hereinafter re ferred to asrefuse") sink. There may, of course, be a layer of water on top of theliquid mass, to minimize loss of sand with the floats.

In U. S. Patent No. 1,392,400, which relates to the Chance method ofseparation, it has been proposed to provide, in the liquid mass in theseparating vessel or chamber, horizontal zones or strata of difi'erentspecific gravity or density, whereby in addition to the light materialor "floats" and the heavy material or "sinks," intermediate products inthe nature of middlings" may be obtained, these middlings" beingextracted continuously by means of a screw conveyor leading themiddlings" to an elevator whereby it is carried above the level of theliquid in the separating chamber, to be thereafter suitably screened orotherwise treated separately. In U. S. Patent No. 1,545,636, alsorelating to the Chance method, it has been proposed to intermittentlywithdraw intermediate products mixed with sand by means of a gate in theside of a cal complications and wear, and that it cannot be appliedconveniently to a separating vessel of circular horizontalsectionalthough the screw conveyor within the chamber may serve a usefulpurpose in assisting agitation of the liquid mass to maintain the sandin suspension.

An object of the present invention is to provide an improved method andapparatus for carrying out the Chance process which is not subject tothese disadvantages.

According to the present invention, the separating vessel or chamberthat contains the separation medium or liquid mass (comprising a su.spension of sand or the like in a liquid) is pro vided with mechanical orother agitating means and with hydraulic jets which not only serve tomaintain the sand or the like in suspension in the liquid, but alsoprovide a plurality of zones of difierent specific gravities in theliquid mass. Discharge or outlet means in the region of at least onesuch zone below the uppermost one are arranged so that in operationmiddlings floating in or on this zone of relatively high specificgravity (as compared with the liquid mass above) are discharged throughsaid outlet by said agitating means, and are lifted in a discharge ductor ducts communicating with said outlet to a suitable level fordischarging said middlings." The hydraulic jets may be arranged toassist in directing the middlings into the outlet; or other water jetsor suitable means may be provided for this purpose. Hydraulic jets (i.e., sand and water or water jets) and/ or mechanical means may beprovided in the duct or ducts for lifting the middliugs; and,preferably, an adjustable weir is provided at the top of the dischargduct(s)or at least one of such ductsfor varying the head of the liquidmass in the duct or ducts.

The separating vessel or chamber may be of any suitable shape or form,and may be of circular horizontal section. In the form of apparatushereinafter described, a mechanical agitator is arranged to rotate abouta vertical axis in the liquid mass, and the discharge or outlet meanscomprises one or more tangential outlets communicating with thedischarge duct or ducts and suitably arranged relative to the directionof rotation of the agitator (i. e., opening out through the peripheralvessel wall in the direction of rotation produced at this intermediatelevel of the liquid mass), so that the middlings, which are directed bythe agitator to the wall of the separating chamber, are discharged intothe said duct or ductsfor removal and subsequent treatment. In otherwords, the agitator may be made to not merely agitate the liquid andkeep the sand in; suspension, but also to rotate the mass at theintermediate level at suilicient velocity to cen-, trifuge to itsperiphery the intermediate material floating in this zone, while theheavier material is allowed to sink through said zone. As alreadymentioned, sand and water jets, or water jets, and/or mechanical meansmay be introduced into the said duct or ducts to assist in lifting the"middlings.

That the heavy material should thus sink right through the zone belowthe top one-instead of mostly or largely discharging at its peripheraloutlet, along with the middlings, by centrifugal action-is explained (1)by the fact that in falling through the top zone where the specificgravity of the fluid mass is the lowest, the heavy material acquiresmuch greater velocity than does the (lighter) middlings; and (2) by thefact that at the zone whose specific gravity corresponds to that of themiddlings, the middlings necessarily lose all their velocity, whereasthat of the heavy material is maintained or even augmented. Accordingly,the accumulated momentum of the falling heavy material carries it veryquickly past the middlings outlet, before the centrifugal force therecan deflect it materially.

The middlings" thus separated both from the coal, which remains floatingat the top of the separating vessel, and from the refuse, which iswithdrawn at the bottom of the separating chamber, may pass from saiddischarge duct or ducts on to the desanding and drainage screen used forthe floats, suitable barriers being provided on the screen formaintaining the separation of the materialsor, of course, they may bedesanded and drained on a separate screen.

One arrangement of apparatus for carrying out the Chance process inaccordance with the invention will now be described by way of examplewith reference to the three figures of the accompanying drawing, inwhich Figure 1 shows a part longitudinal section; Figure 2 shows a planof the apparatus; and Figure 3 shows a part longitudinal section ofapparatus having mechanical means for lifting the middlings" in theduct.

Referring now to Figures 1 and 2 of the drawing, the separating chambercomprises a vessel I of inverted conical shape having a cylindrical topportion 2 which is provided with the usual overflow weir 3 through whichpass the floats. A discharge chamber 4 is provided at the bottom of thevessel, for discharging the refuse from the vessel. At a suitableposition or level intermediate between the weir 3 and the dischargechamber 4, and preferably (as shown) in the conical portion of thevessel I, there is arranged a tangential outlet 5 communicating with anupward directed pipe 6 which terminates above a chute 1 leading to themain desanding and draining screen 8 for the floats from the weir 3-thesaid screen 8 being divided by a partition 9 so that the floats" and themiddlings" are discharged from said screen separately.

Water is introduced through jets I4 in the side of the vessel l at threedifferent planes or levels, two below and one above the said tangentialoutlet 5. The quantities of water introduced at these planes are soarranged or determined that the density of the liquid mass in the vesselbecomes progressively (but not necessarily uniformly) greater from topto bottom. Thus for example it may be arranged that the density in thezone above the top plane is about 1.45, while in the intermediate zonebetween said top plane and the next lower plane it is about 1.75, and inthe zone below the bottom plane the density is greater than 1.75.

Rotation of the liquid mass is effected to a great extent by an agitatorcomprising a shaft I0 and stirring arms ll, mounted to rotate about avertical axis, and the agitator is arranged so that materials sinkingthrough the liquid mass are directed to the side of the vessel. The armson the agitator are positioned so that the "middlings (that is to say,those materials which are of a specific gravity intermediate between the"low or coal gravity and the high or refuse gravity) are directed intothe tangential outlet 5 and up the pipe or duct 6 attached thereto, Inthe outlet 5 and the pipe 6, a number of suitably directed sand andwater or water jets l2 are provided to assist in conveying and raisingthe middlings to the chute l which directs them on to the screen 8. Atthe termination of the pipe 8, an overflow weir I3 is arranged, and isprovided with suitable means of adjustment so that the hydraulic head ofmaterial and liquid in the pipe 6 can be balanced against thecorresponding head of material and liquid in the vessel l above theoutlet 5. As shown, the vertically movable weir I3 is attached toslotted guide bars l6, one at least of which may be clamped to a sidewall of the weir-box by a clamp-bolt arrangement ll. The balancedconditions thus obtained substantially prevent the liquid mass in thevessel I from flowing out of the outlet 5, so that the upward currentsof agitation are maintained, and the sand is kept in suspension to formthe zones of varying specific gravity.

Mechanical means for lifting the middlings may be provided in the pipe6, in addition to or in place of the sand and water or water jets l2.The mechanical means may comprise an elevator l5 in the pipe 6, as shownin Figure 3 of the drawing.

While the invention is particularly designed for the cleaning of coal,it may be applied to the separation of other materials which areseparable by the Chance process, and the word coal" used herein isintended to include such materials. The term liquid mass we desire to beunderstood to include any mixture of comminuted solids and liquids whichwhen properly agitated will approach the properties and fluidity of aliquid; the term water" is intended to mean any liquid suitable formaking a liquid mass of the described type; and the term sand" isintended to designate any comminuted solid insoluble or substantiallyinsoluble in the liquid used and suitable for making a liquid mass ofthe described type.

Having thus described our invention, we claim: 1. An improved process ofseparating heavy. intermediate and lighter materials by means of aliquid mass of sand or the like maintained in suspension in and by anupfiow of liquid, which comprises supplying upflowing liquid to theliquid mass at various levels so as to maintain therein stratified zonesof various different densities, in the upper and intermediate of whichzones the lighter and intermediate materials respectively float and arethus arrested and segregated, while the heavier material sinks through;discharging the lighter material at the top of the liquid; rotating themass in the zone of intermediate density at sufficient velocity tocentrifuge to its periphery the intermediate material arrested in thezone as aforesaid; continuously expelling the centrifuged intermediatematerial from the periphery of said intermediate zone; and subjectingthe expelled intermediate material to fluid current action to lift itthrough a segregated portion of the liquid mass outside the field ofrotation for discharge at the level of the liquid in said segregatedportion.

2. Apparatus for the separation of heavy, intermediate and lightermaterials by means of a liquid mass of sand or the like maintained insuspension by an agitated upflow of liquid, in which mass the lighter ofthe materials which is to be separated floats at the top while the restsinks lower in the mass, said apparatus comprising a separating vesselhaving a discharge for the lighter material at its top, a discharge forthe heavier material at its lower region, and an outlet for theintermediate material at an intermediate point; an open conduit inconstant communication at its bottom with the vessel and leading upwardfrom the outlet substantially to the level of the top of the vessel;means for supplying upfiowing liquid to the mass at various levels, soas to maintain the liquid mass in the vessel in stratified zones ofvarious different densities; agitating means for maintaining the sand insuspension in the liquid in said zones and for rotating the mass in thezone of intermediate density at sufficient velocity to centrifuge to itsperiphery intermediate material sinking to this zone and remainingthere, while the heavier material sinks therethrough, and for causingcentrifugal expulsion of the intermediate material through said outletand into said conduit; and fluid current means operative to elevate theintermediate material in said conduit for dis charge from the topthereof.

3. Apparatus for the separation of heavy, in-

iermediate and lighter materials by means of a liquid mass of sand orthe like maintained in suspension by an agitated upfiow of liquid, inwhich mass the lighter of the materials which is to be separated floatsat the top while the rest sinks lower in the mass, said apparatuscomprising a separating vessel having a discharge for the lightermaterial at its top, a discharge for the heavier material at its lowerregion, and an outlet for the intermediate material at an intermediatepoint; an open conduit in constant communication at its bottom with thevessel and leading upward from the outlet substantially to the level ofthe top of the vessel; means for supplying upfiowing liquid to the massat various levels. so as to maintain the liquid mass in the vessel instratified zones of various diiTerent densities; agitating means formaintaining the sand in suspension in the liquid in said zones and forrotating the mass in the zone of intermediate density at suflicientvelocity to centriiuge to its periphery intermediate material sinking tothis zone and remaining there, while the heavier material sinkstherethrough, and for causing centrifugal expulsion of the intermediatematerial through said outlet and into said conduit; and jet means atvarious points along the conduit operative to elevate the intermediatematerial in said conduit for discharge from the top thereof.

FRANK LOUIS GRIFFITHS. FREDERICK CHARLES MEYER.

wit i mm

